Field of the Invention
This invention concerns the supporting of glass sheets in a vertical or substantially vertical position during the various treatments to which the glass sheets are subjected for the purpose of curving and/or toughening them, notably for the purpose of their reheating, curving (for example by pressure), thermal toughening and conveying between the various treatment stations. The invention also concerns a device for curving by pressing, cooperating with a support device. It can be applied primarily to the production of curved and toughened glazings of large dimensions having a very pronounced curvature.
Description of the Related Art
In the technology of curved, toughened panes, the quality criteria currently most commonly demanded are strict conformity with the specified curvature, a degree of toughening or tempering corresponding to a desired increase in mechanical strength for the purpose of assuring that any breakage is in conformity with safety standards, an optical quality which excludes any mottling effect and, finally, complete absence of any imprint left by the tools used during the various treatments and markings from tongs which support the pane during vertical treatments.
This latter requirement has favored the development of processes for curving and toughening that operate on a glass sheet held horizontal or substantially horizontal. However, it is impossible to convert a vertical apparatus into a horizontal apparatus; moreover, conventional production lines are of the vertical type and, with the exception of the problem of tong markings, are in no way obsolete from the aspect of the quality of the glazing produced and of the diversity and complexity of the shapes which these vertically operating processes make possible.
Many publications deal with means for holding glass sheets designed for acting only on the edge of the sheets. Thus, there is known, for example from the U.S. Pat. Nos. 2,134,797 and 2,537,803 a curving process according to which the glass sheets are disposed in a frame which holds them by a series of lugs or forks bearing against the different sides of the pane. It has also been proposed, in U.S. Pat. No. 3,298,809 to cause the lower edge of the glass sheet to rest an the horizontal cross-member of a frame and to retain the upper edge by a bearing bar cooperating with locking components.
The fundamental problem in all of these means of support is that the glass sheet can very easily become detached from them, the support being achieved simply by maintaining the stability of the vertical equilibrium position. This is especially true when the support means are generally of small dimensions, in order not to interfere with reheating and/or cooling during the thermal toughening. Moreover, gripping by lugs is possible only if the glass sheet effectively exerts a counter-action, which assumes that it does not subside or curve excessively during heating.
European Patent EP-B-126 687 proposes a frame, of which the holding means being applied against the upper edge of the glass sheet are freely mounted in the vertical direction by means of a lateral guide. These holding means, for example of the piston type, can thus accompany the glass sheet and continue to hold it even when it commences to sag. Furthermore, these holding means can be coupled with tongs, the jaws of which do not close unless the glass sheet escapes from the piston, thereby catching said sheet and preventing it from falling and breaking and allowing it to be removed from the furnace so that the latter is not encumbered with glass debris.
In practice, the frame according to EP-B-126 687 gives good results with small panes, i.e., with panes having a height of less than 600 mm. For greater heights, the subsidence during heating is too great and the jaws regularly come into action to seize the glass sheets, which, although it allows them to be removed from the curving, toughening apparatus, causes markings from tongs.
But even if few panes have all dimensions greater than 600 mm, it is not common for the desired shape to require a positioning of the pane in the frame such that its height corresponds to its largest dimension, which frequently exceeds 1000 mm. The problem especially arises when the pane comprises at least one very curved portion, which requires the use of a curving press in which the female mold is composed of elements assembled with one another and pivotal about assembly axes, the median element being initially the only one to be applied against the glass sheet and the pressing operation continuing by the progressive application of the lateral elements. It will be readily understood that if it is desired that the glass sheet shall not warp or even slide during pressing (these phenomena would at worst result in falling of the glass sheet and, in the most favorable cases, lead to faults in curvature and the development of optical defects), it is essential that the axes of pivoting be vertical. In other words, the shape desired after curving determines the orientation of the pane in the frame.